title: Synthesis, structural characterization, and thermoresponsivity of hybrid supramolecular dendrimers bearing a polyoxometalate core.
abstract: A series of cationic dendrons bearing triethylene glycol monomethyl ether terminal groups of different generations have been synthesized and used to encapsulate an inorganic polyanionic cluster [K(12.5)Na(1.5)(NaP5W30O110)] through electrostatic interactions. The resulting dendritic cation-encapsulated polyoxometalate (POM) complexes, cluster-dendrimers, are soluble in water and exhibit lower critical solution temperatures (LCST). The thermoresponsivities of these complexes in aqueous solutions were studied by turbidimetry and variable-temperature (1)H NMR spectroscopy. The observed cloud points show a remarkable dependence on the generation of the dendrons. Complexes composed of first-generation dendrons exhibit no obvious thermoresponsive properties, but for complexes bearing second-generation dendrons, the LCST decreases as the number of dendritic cations around the POM cluster increases. Complexes composed of third-generation cations underwent reversible aggregation and disaggregation upon heating and cooling, respectively. This thermally induced self-aggregation was characterized by DLS and TEM. In addition, the effects of salt and solvent on the LCST were investigated. This research demonstrates a new type of thermoresponsive dendritic organic-inorganic hybrid complex and provides a general route to the endowment of POMs with temperature-sensitive properties through electrostatic interactions.
authors.affiliation: State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun 130012, P.R. China.
authors.forename: Hailong
authors.initials: H
authors.lastname: Chen
authors.forename: Yang
authors.initials: Y
authors.lastname: Yang
authors.forename: Yizhan
authors.initials: Y
authors.lastname: Wang
authors.forename: Lixin
authors.initials: L
authors.lastname: Wu
keywords: aggregation; dendrimers; polyoxometalates; salt effect; supramolecular chemistry